On Thu, Sep 17, 2020 at 11:23:59AM -0700, Jesse Brandeburg wrote: > Nitesh Narayan Lal wrote: > > > In a realtime environment, it is essential to isolate unwanted IRQs from > > isolated CPUs to prevent latency overheads. Creating MSIX vectors only > > based on the online CPUs could lead to a potential issue on an RT setup > > that has several isolated CPUs but a very few housekeeping CPUs. This is > > because in these kinds of setups an attempt to move the IRQs to the > > limited housekeeping CPUs from isolated CPUs might fail due to the per > > CPU vector limit. This could eventually result in latency spikes because > > of the IRQ threads that we fail to move from isolated CPUs. > > > > This patch prevents i40e to add vectors only based on available > > housekeeping CPUs by using num_housekeeping_cpus(). > > > > Signed-off-by: Nitesh Narayan Lal <nitesh@xxxxxxxxxx> > > The driver changes are straightforward, but this isn't the only driver > with this issue, right? I'm sure ixgbe and ice both have this problem > too, you should fix them as well, at a minimum, and probably other > vendors drivers: > > $ rg -c --stats num_online_cpus drivers/net/ethernet > ... > 50 files contained matches Ouch, I was indeed surprised that these MSI vector allocations were done at the driver level and not at some $SUBSYSTEM level. The logic is already there in the driver so I wouldn't oppose to this very patch but would a shared infrastructure make sense for this? Something that would also handle hotplug operations? Does it possibly go even beyond networking drivers? Thanks. > > for this patch i40e > Acked-by: Jesse Brandeburg <jesse.brandeburg@xxxxxxxxx>
